Polyalkylene glycols (PAG) comprised of random copolymers of ethylene oxide (EO) and propylene oxide (PO) are known to provide excellent friction control (i.e., low coefficients of friction) when used as base oils in lubricant formulations. The friction performance of such EO/PO PAGs is significantly superior to that of mineral oils, synthetic hydrocarbons and PAG polymers that are based on PO, butylene oxide (BO) or combinations thereof. High performance EO/PO random copolymer containing PAGs typically contain 50-60% by weight of units derived from EO. PAGs which are used in known lubricant formulations are PAGs produced using monol (e.g. butanol), diol (e.g. propylene glycol) or triol (e.g. glycerol) initiators.
EO/PO PAGs are typically used as the primary base oil in gear, calendar and bearing lubricants. For example, such PAGs are used at levels >50% by weight and more often at levels >95%.
A key trend in the industry is to develop more energy efficient lubricants by selecting base oils which can offer better friction control. Friction coefficients of EO/PO PAGs can be further lowered by increasing the EO-derived content of the polymers. However, increased levels of units derived from EO negatively impact the pour points of the EO/PO PAG. Thus, polymers with a content of units derived from EO of 75% have limited practical use as primary base oils in gear lubricants due their high pour points.
There remains a need for EO/PO PAGs with sufficiently high content of units derived from EO so as to provide lower coefficients of friction compared to conventional EO/PO PAGs while at the same time possessing acceptable low temperature properties, such as pour point. It would be further desirable that the EO/PO PAG remain clear, homogeneous and stable across a broad temperature range, such as from 50° C. to −25° C.